Method of making a polymer and wood flour composite extrusion

ABSTRACT

An extrusion profile is formed of foamed plastic, which includes a filler of wood flour or wood fiber. The foamed plastic may include polyvinyl chloride, chlorinated polyvinyl chloride or polystyrene in combination with the wood flour filler.

This application is a divisional of application Ser. No. 08/748,201, filed Nov. 12, 1996. This application claims the benefit of U.S. Provisional Application No. 60/017,756, filed May 16, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to polymer extrusion and injection molded products and processes. The invention has particular application to a polymer extrusion or injected molded polymer that includes an addition of wood flour as an ingredient to the composite material.

As a result of the increasing cost of wood and the attendant cost of wood frames, there is a demand for alternatives to solid wood construction products. Accordingly, the use of plastic extrusion profiles as substitutes for wood products in the area of picture frames and door, wall and window frames and moldings has increased in recent years. Injection molded plastic has also been utilized in the furniture industry for forming plastic chairs, lounges, tables and the like.

Polymer extrusions are well-known for use in forming components for window and door frames. Plastic extrusion profiles are commonly formed with polymer materials such as polyvinyl chloride and chlorinated polyvinyl chloride (PVC and CPVC), polystyrene, acrylonitrile-butadiene-styrene (ABS) or similar materials. Polymer materials are conventionally used in combination with a variety of fillers, lubricants and pigments. Additionally, for foamed polymers, a blowing agent is also added to the composite. An example of a foamed extrusion is found in commonly assigned U.S. Pat. No. 5,508,103, entitled "Extrusion Product with Decorative Enhancement And Process Of Making The Same."

As a result of the increasing cost of polymer materials, there exists a need for less expensive filler materials, which can be used with polymers such as PVC, but do not adversely affect the strength or wear resistance of the resulting profile. One such filler material that has been given increasing consideration is wood flour or wood fiber. Polyvinyl chloride thermoplastic polymer materials have been combined with wood and wood fiber to make extruded or injection molded materials.

Various patents and publications have proposed extrusion and injection molded materials that combine polymers and wood fibers. One example of such a patent is U.S. Pat. No. 5,406,768, assigned to Andersen Windows. The '768 patent describes a structural component made of polymer and wood fiber in which the polymer is rigid PVC. While rigid PVC has many uses, the present invention is directed primarily to the use of a composite with foam PVC. The extrusion of foamed PVC, includes a blowing or foaming agent. Addition of foaming agents can also affect the ability to add wood flour fillers. However, the use of foamed PVC has advantages over rigid PVC in that the less-dense foamed material allows substantial cost savings in the amount of PVC used in the composite. U.S. Pat. Nos. 5,082,605 and 5,088,910 also describe composite materials formed from polymers and wood or cellulose fibers.

One difficulty presented by additions of wood flour is the absorption of moisture by the wood flour. The loss of moisture within the extrudate can slow the extrusion rate as a result of an increase in viscosity. Another difficulty involves foaming or expansion of the extrudate with the wood flour. The wood flour particles do not expand or foam and, thus, the foaming must be done around the wood flour particles. Also, unlike polymers such as PVC, the addition of heat to wood flour does not improve flowability of the extrudate.

The present invention overcomes these difficulties by a two step process in which the wood flour particles are encapsulated by the resin and pelletized. The pelletized pieces are then mixed with additional resin and blowing agents. It is believed that the encapsulation process prevents moisture absorption and permits foaming of the extrudate. Additionally, the encapsulation provides a smoother skin in the final product.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a composite of a polymer and wood flour for formation of an extrusion profile. The profile has use in moldings, window and door frames and similar types of applications. The composite material includes an addition of wood flour mixed with the polymer. The mixture is extruded into a formed profile through an extruder and vacuum tank or shaper.

Prior to extrusion, the wood flour is encapsulated by polymer and then pelletized. After mixing additional polymer with the pelletized product, and the addition of blowing agents, the product is extruded into a final profile. The vacuum tank and shaper help maintain the profile shape as the cellular extrudate expands.

The composite of the present invention can include various types of polymers. Several examples are presented of preferred embodiments in which the polymer comprises PVC, CPVC and polystyrene. The PVC, CPVC and polystyrene are preferably added to the blend in the form of standard, commercially available resins, which include plasticizers to permit flexibility in the final product. The composite also includes an amount of wood flour as well as process aids, stabilizers, lubricants, and colorants and a blowing agent.

The process of the present invention utilizes an extruder in conjunction with a vacuum tank or shaper. The extrusion material is extruded through a die and into the shaper or vacuum tank. The material expands or foams as it enters the shaper and is cooled. The extrusion profile leaves the vacuum tank or shaper in a hardened form, which then fully hardens and cools.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, one should refer to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention. In the drawings, which are not to scale:

FIG. 1 is a schematic diagram showing the sequence of operations in the final extrusion process of the present invention with polyvinyl chloride and wood flour extrusion material;

FIG. 2 is a schematic diagram showing the sequence of operations in the final extrusion process of the present invention with polystyrene and wood flour extrusion material;

FIG. 3 is a longitudinal sectional view of the end of an extrusion machine with a die and shaper;

FIG. 4 is a cross-sectional view of the profile that emerges from the shaper of FIG. 3 illustrating, schematically, the wood flour particles;

FIG. 5 is a perspective view of a picture frame profile extruded with the composite of the present invention.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present invention provides a composite of a polymer and wood flour for formation of an extrusion profile. The profile has use in moldings, window and door frames and similar types of applications.

The composite material of the present invention can include various types of polymers in combination with the wood flour filler addition. Several examples are presented of preferred embodiments in which the polymer comprises PVC, CPVC and polystyrene. The PVC, CPVC and polystyrene are preferably added to the blend in the form of standard, commercially available resins, which include plasticizers to permit flexibility in the final product. The composite also includes an amount of wood flour as well as process aids, stabilizers, lubricants, colorants and a blowing agent. The profile material is typically used in a picture frame or door, window, wall or other molding, and thus preferably includes component materials that provide high strength and durability.

The wood flour addition is preferably hardwood in the form of sawdust. The wood flour is ground to a preferred particle size in which 0% to 10% is 425 microns; 35% to 80% is 250 microns; and 15% to 50% is 180 microns. Moisture is preferably controlled in the wood flour to approximately between 3% and 6%.

The materials are formed into an extrudable mixture by combining various ingredients with a high intensity mixer at the appropriate temperature. Resins, fillers and modifiers may be added to the mixture. The extrusion mixture is then formed into a profile by pulling the mixture through an extrusion die and shaper.

Before the addition of wood flour, the polymer resin is blended with additional ingredients in a standard Henschel blender or mixer. In a polystyrene composite of the present invention, crystal polystyrene (CPS) and high impact polystyrene (HIPS) are added to the blender at low speed. Mineral oil, which acts as a wetting agent, is added and blended for approximately 30 seconds followed by the addition of stearic acid, which acts as a lubricant, which is added and blended for approximately another 30 seconds. Titanium dioxide, which acts as a colorant, is optionally added at this time. Full mixing of this mixture with CPS requires approximately 4 minutes total.

Alternatively, PVC and CPVC may be used in which case they are added to the Henschel blender at a temperature of approximately 100° F. and mixed at high speed. The other ingredients are added to the PVC and CPVC blend as explained above for CPS. The PVC and CPVC are mixed to a temperature of approximately 200° F. and then cooled to approximately 150° F.

In the above-described preparation of the resin mixture, the resin is added to the wood flour in a continuous mixing machine and then extruded and pelletized in a pelletizer machine. In this first extrusion to form pellets, blowing agent is not used. Thus, the initial pelletizing extrusion does not include foaming of the polymer blend. The ingredients are preferably added to the mixer hopper by conveyors so that the conveyor rates may be adjusted to add the appropriate amount of each ingredient to the mixture. Thus, the polymer resin compound is added to the continuous mixing machine by one conveyor while the wood flour is added to the continuous mixing machine by another conveyor. Additional conveyors may be used for the additional ingredients, such as lubricants and colorants.

The materials are mixed together in the mixer section of the continuous mixing machine. The fused material has a melt temperature of approximately 350° F. to 450° F. It is understood that sufficient mixing is important to cause encapsulation of the wood flour particles by the polymer resin. The fused material is heated in the continuous mixer machine to the melt temperature where it forms a continuous rope and is then dropped onto the screw extruder section of the continuous mixer machine. Control of the melt temperature of the continuous rope is important to prevent degradation of the extrudant. The melt material then exits the extruder section of the mixer machine through a strand die with approximately 210 openings. The melt proceeds through the strand die and the strands are pelletized by a dry face pelletizer. Again, temperature control through the extruder and strand die is important to prevent degradation of the extrudant. Pellets of material are preferably formed is a size approximately 0.015 inch in length and a diameter of approximately 0.015 inch. Of course pellet size may be increased or decrease by adjustment of the speed of the pelletizing cutter.

The pellets are preferably moved from the cutting area to a cooling chamber by compressed air. The pellets then move through the cooling chamber by chilled compressed air and are discharged into storage vessels. Control of the moisture content of the pellets is also important to assure the quality of the composite. At the end of the pelletizing process, the pellet moisture content should be less than 1% moisture.

As presently understood, the polymer resin (PVC, CPVC or PS) coats the surface of the wood fiber particles. While some resin may penetrate the surface of the fiber, on account of the jagged surface of the fiber particles, the present process is understood to encapsulate or provide a coating about the wood fiber particles with the polymer resin and prevent or minimize the penetration of moisture into the fiber particle.

Only a portion of the total desired amount of resin is used in making the pellets. The remainder of the resin is added when making the final extrusion composite. For example, in a composite having 100 parts total of PVC resin, only 40 parts resin will be added to the mixture to form the pellets. The remaining 60 parts resin will be added in forming the final product. Of course, the PVC is only a portion of the commercially available PVC resin. Similarly, polystyrene is a portion of commercially available polystyrene resin, which is used in the composite of the present invention.

After preparation of the polymer and wood fiber pellets, the pellets are blended into a compound with additional polymer resins for use in making the final extrusion profiles. The polymer/wood fiber pellet is added to a mixer with additional polymer resin. In the case of PS and wood flour, CPS and HIPS are added to a Henshel mixer at low speed along with the addition of the PS/wood flour pellets. At 30 second intervals, additions are made of mineral oil, then blowing agents and nucleating agents and finally the remaining ingredients. The mixture is blended for about 4 minutes at low speed and then dumped into a bin.

In the case of PVC or CPVC and wood flour, the pellets are added to a Henshel mixer at high speed along with PVC or PVC and CPVC resin at a temperature of approximately 100° F. Additional ingredients are added as the temperature is increased. Stabilizer is added at 150° F., followed by filler, process modifiers and process aids at 160° F. and, finally, lubricants and blowing agents at 180° F. When the mixture reaches approximately 200° F., the mixture is dumped into a cooler and allowed to cool to approximately 150° F.

Schematic diagrams that illustrate two preferred sequences of preparation of the final extrusion profile of the present invention are shown in FIGS. 1 and 2. In FIG. 1, an extruder 10 is used in conjunction with a vacuum tank 12. A puller 20 acts to pull the extruded profile onto a cut-off table 22. The process sequence shown in FIG. 1 is used with the polyvinyl chloride and wood flour extrusion material.

A second sequence of preparation is shown in FIG. 2. In this sequence, the extruder 24 is followed by a shaper 26, puller 34 and cut-off table 36. This process sequence is used with polystyrene and wood flour extrusion material. In each sequence, the extruded profile 58 is pulled through the die and formed.

As shown in more detail in FIG. 3, extrusion of the above-described mixtures is accomplished by use of an extruder 40 with a body 42, worm 44 and die 46. The worm acts to force the extrusion material through the die and shaper 48. The shaper includes a cylindrical sleeve 50 with a smooth guide wall. The shaper has substantially the same cross-sectional shape as the die. The shaper preferably includes a heat controlling jacket 52 with a connection 54 to enable a temperature regulating fluid, such as water, to be contained within the jacket.

The puller, shown in FIG. 1, acts to draw the extruded profile 58 from the shaper. The composition of extrudable material is prepared and introduced into the extrusion machine through channel 60. The material is pushed through the die, where it only slightly expands, and then begins to fully expand as it enters the shaper 48. The jacket 52 of the shaper 48 is kept at a temperature lower than the softening point of the extrusion material. As the material contacts the inside wall of the shaper, it begins to harden from the outside surface to the inner core.

The material beings to expand or foam as it passes through the die and then it begins to fully expand as it enters the shaper. A vacuum draw on the shaper helps maintain the profile shape as the cellular material expands. The material cools as it passes through the shaper and forms its desired shape. A puller acts to draw the extruded profile from the shaper. The profile achieves a cross-section that is substantially the same as the cross-section of the outlet of the shaper. The temperatures of the die and shaper as well as the speed of the extrusion profile are parameters that affect the properties of the resulting product. A space of several inches may be present between the die exit and the shaper entrance in order to allow some expansion of the extrudate before entering the shaper.

Specifically, for the above-described PS extrusion material, the extruder temperatures are preferably as follows: zone no. 1: 280-310° F.; zones nos. 2, 3, 4: 290-350° F.; zone no. 5: 320-360° F. and the die: 300-350° F. In contrast, for the above-described PVC and CPVC the extruder temperatures are preferably as follows: zone no. 1: 290-330° F.; zones nos. 2, 3, 4: 300-360° F.; zone no. 5: 320-375° F. and the die: 320-375° F. The temperatures of zone no. 1 must be sufficiently high to provide strong forward movement of the extrusion material, but not too high so as to cause slippage of the material on the extruder screw. The temperatures of zones nos. 2, 3 and 4 must be regulated to continue proper forward movement of the melt as it becomes a homogeneous mixture to insure a suitable density of the foamed profile. Finally, the temperature of the die is important for the foam to expand to the proper size of the shaper.

The cross-section of the extrusion profile of one embodiment of the present invention is shown in FIG. 4. A hard skin 66, 68 may be formed on the outer portion of the profile 70. The remaining portions 72, 74 of the profile may include a hardened skin or may be left without a hard skin, as desired. FIG. 4 also illustrates the encapsulated wood fibers 73 within the cellular matrix 75 of the profile.

One example of a completed profile for a picture frame is shown in FIG. 5. The profile includes a decorative portion 76 as well as hardened skin portions 78, 80. After the profile is cured and hardened, various finishes may be applied to the profile to enhance and highlight the profile. For example, the profile may be painted, stained, glazed, brushed or clear coated. Hot foil stampings may also be applied for further decorative effect.

Using the above-described process, pellets were prepared and extruded into profiles. A PVC/wood flour pellet was prepared using a portion of the total amount of 100 parts PVC resin with the following formulation:

    ______________________________________     Ingredient Parts    Description     ______________________________________     PVC Resin  up to 100                         Resin     Mark 1924  2        Tin Stabilizer     Kaneka K12 7        Acrylic Process Aid     Calcium Carbonate                4        Filler     Wood Flour 15 to 60 Wood Fiber Filler     Calcium Sterate                1        Lubricant     Loxiol 1875                1.5      Ester Lubricant     AC-629A    0.1      Oxidized Polyethylene Wax Lubricant     ______________________________________

The PVC/wood flour pellets were blended to form an extrudable compound with the remaining PVC resin and blowing agent with the following formulation:

    ______________________________________     Ingredient   Parts      Description     ______________________________________     PVC Resin    100        Resin     Mark 1924    2          Tin Stabilizer     Kaneka K12   7          Acrylic Process Aid     Calcium Carbonate                  4          Filler     PVC/Wood Flour Pellet                  15 to 60   Wood Flour Filler     Calcium Sterate                  1          Lubricant     Loxiol 1875  1.5        Ester Lubricant     AC-629A      0.1        Oxidized Polyethylene Wax                             Lubricant     Hughes HRVP 01                  .2 to .7   Blowing Agent     Titanium Dioxide                   0 to 10   Whitener     ______________________________________

Pellets of a CPVC/wood flour blend were prepared with the following formulation:

    ______________________________________     Ingredient Parts    Description     ______________________________________     PVC Resin  up to 40 Resin     C-PVC Resin                up to 60 Resin For HDT performance     Mark 1924  3.5      Tin Stabilizer     Kaneka K12 7.45     Acrylic Process Aid     Titanium Dioxide                10       Colorant     Wood Flour 15 to 65 Wood Flour Filler     Calcium Sterate                1.05     Lubricant     VGE-1875   1.68     Ester Wax Lubricant     AC-629A    0.82     Oxidized Polyethylene Wax Lubricant     ______________________________________

The CPVC/wood flour pellets were blended to form an extrudable composite with the following formulation:

    ______________________________________     Ingredient    Parts    Description     ______________________________________     PVC Resin     40       Resin     C-PVC Resin   60       Resin For HDT performance     Mark 1924     3.5      Tin Stabilizer     Kaneka K12    7.45     Acrylic Process Aid     Titanium Dioxide                   10       Colorant     CPVC/Wood Flour Pellet                   15 to 65 Wood Flour Filler     Calcium Sterate                   1.05     Lubricant     VGE-1875      1.68     Ester Wax Lubricant     AC-629A       0.82     Oxidized Polyethylene Wax                            Lubricant     Hughes HRVP 01                   .2 to .7 Blowing Agent     Titanium Dioxide                    0 to 10 Whitener     ______________________________________

Pellets of a polystyrene/wood flour blend were prepared with the following formulation:

    ______________________________________     Ingredient    Parts     Description     ______________________________________     Crystal Polystyrene                   up to 70  Resin     High Impact Polystyrene                   up to 30  Resin For Impact Strength     Mineral Oil   .22       Wetting Agent     Stearic Acid  .03       Lubricant     Wood Flour    60 to 140 Wood Flour Filler     ______________________________________

The polystyrene/wood flour pellets were blended to form an extrudable composite with the following formulation:

    ______________________________________     Ingredient    Parts     Description     ______________________________________     Crystal Polystyrene                   70        Resin     High Impact Polystyrene                   30        Resin For Impact Strength     Mineral Oil   .22       Wetting Agent     Stearic Acid  .03       Lubricant     PS/Wood Flour Pellet                    60 to 140                             Wood Flour Filler     Sodium Bicarbonate                   .5 to .8  Blowing Agent     Citric Acid   .1 to .2  Activator     Titanium Dioxide                    0 to 10  Whitener     ______________________________________

The above ingredients in each example were blended and utilized to form an extrusion profile, as described above.

While several embodiments of the invention are illustrated, it will be understood that the invention is not limited to these embodiments. Those skilled in the art to which the invention pertains may make modifications and other embodiments employing the principles of this invention, particularly upon considering the foregoing teachings. 

What is claimed is:
 1. A method of forming a solid elongated member of predetermined profile for use as a door, window or frame molding, comprising the steps of:encapsulating wood flour particles with a polymer resin in an extrudable material by high intensity mixing, said extrudable material consisting essentially of, in parts (volume):

    ______________________________________     polymer resin:   in an amount of up to 100     wood flour:      15-140     stabilizers:     in an amount up to 5     lubricants:      in an amount up to 5     process aids:    in an amount up to 10,     ______________________________________

extruding and cutting said extrudable material to form pellets of said extrudable material, mixing additional polymer resin and a non-aqueous blowing agent with said pellets to form an extrudable foam material, compressing said extrudable foam material at a compression stage by passage through an orifice, said orifice having at one end thereof a predetermined profile, said foam material consisting essentially of, in parts (volume):

    ______________________________________     polymer resin:   in an amount up to 100     wood flour:      15-140     stabilizers:     in an amount up to 5     lubricants:      in an amount up to 5     process aids:    in an amount up to 10     blowing agents:  .2 to 5     ______________________________________

expanding said foam material through a shaper, said shaper having an internal solid surface defining a channel for said foam material, and solidifying said foam material to form a solid elongated member.
 2. The method of claim 1 wherein said expansion of said foam material causes the formation of air pockets around said encapsulated wood flour particles.
 3. The method of claim 1 wherein said wood flour particle size comprises, in parts (volume):

    ______________________________________     up to 10%          about 425 microns,     about 40%-75%      about 250 microns,     about 15%-50%      about 180 microns.     ______________________________________


4. The method of claim 1 wherein said elongated member is a frame for a picture.
 5. The method of claim 1 wherein said polymer resin is from the group of polyvinyl chloride, chlorinated polyvinyl chloride and polystyrene.
 6. The method of claim 5 wherein said foam material further comprises, in parts (volume):

    ______________________________________     polyvinyl chloride    100     wood flour            15 to
 60.     ______________________________________


7. The method of claim 5 wherein said foam material further comprises, in parts (volume):

    ______________________________________     chlorinated polyvinyl chloride                               60     polyvinyl chloride       
 40.     ______________________________________


8. The method of claim 5 wherein said foam material further comprises, in parts (volume):

    ______________________________________            polystyrene   100            wood flour    60 to
 140.     ______________________________________ 